For example, in nuclear paraphernalia, a pipe is regularly inspected by an inspection device in order to ensure safety and reliability thereof. Then, when a surface defect such as a crack caused by a secular change occurs or when it is determined that a surface defect caused by a secular change occurs at a welding portion of a nozzle of the pipe as a result of the inspection, there is a need to cut or repair a concerned portion by a processing device. Such a processing device that inspects or processes the pipe is inserted from an opening portion of the pipe as a subject, but it is preferable to insert the processing device so that the processing device passes through the center of the pipe in order to inspect or process the pipe with high precision. In the nuclear paraphernalia, since the pipe is inspected or processed under a radiation environment, it is preferable to move the processing device by a remote operation in consideration of safety, but particularly, in a pipe with a relatively small diameter, it is difficult to insert the processing device so that the processing device passes through the center of the pipe by the remote operation.
In the related art, for example, a pipe inspecting device and a pipe inspecting method described in Patent Literature 1 are simply used to accurately dispose an ultrasonic sensor at the center of the pipe to detect a flaw with high precision. Then, in the device which includes an ultrasonic sensor, a driving unit, a position control unit, and an ultrasonic transmission and reception control unit and detects a flaw in a substantially cylindrical pipe, the sensor is disposed such that the pipe axis matches the sensor rotation axis and is rotated while scanning the pipe so as to detect a flaw on a pipe inner face in the radial direction. Here, the device further includes a position correcting unit which calculates the position of the pipe axis based on an ultrasonic signal, an ultrasonic propagation time, and position information of the sensor obtained by the scanning of the sensor while transmitting an ultrasonic wave in a direction perpendicular to the axis from the sensor disposed at a position assumed as the axis of the pipe before detecting the flaw and generates and transmits a control signal for correcting the position of the sensor to the position of the calculated pipe axis.